Basecamp's Google Sign-In adds Google sign-in to Rails applications. Prior to version 1.3.1, it is possible to redirect a user to another origin if the "proceed_to" value in the session store is set to a protocol-relative URL. Normally the value of this URL is only written and read by the library or the calling application. However, it may be possible to set this session value from a malicious site with a form submission. Any Rails applications using the google_sign_in gem may be vulnerable, if this vector can be chained with another attack that is able to modify the OAuth2 request parameters. This issue has been patched in version 1.3.1. There are no workarounds.

Basecamp's Google Sign-In adds Google sign-in to Rails applications. Prior to version 1.3.0, it is possible to craft a malformed URL that passes the "same origin" check, resulting in the user being redirected to another origin. Rails applications configured to store the flash information in a session cookie may be vulnerable, if this can be chained with an attack that allows injection of arbitrary data into the session cookie. This issue has been patched in version 1.3.0. If upgrading is not possible at this time, a way to mitigate the chained attack can be done by explicitly setting SameSite=Lax or SameSite=Strict on the application session cookie.